U.S. patent number 6,873,489 [Application Number 10/107,832] was granted by the patent office on 2005-03-29 for method, system, and program for estimating coil resistance of a voice coil motor in a disk drive system.
This patent grant is currently assigned to Hitachi Global Storage Technologies Netherlands B.V.. Invention is credited to Peter Kui Ho, Mantle Man-Hon Yu.
United States Patent |
6,873,489 |
Ho , et al. |
March 29, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Method, system, and program for estimating coil resistance of a
voice coil motor in a disk drive system
Abstract
Provided are a method, system, and program for estimating coil
resistance of a voice coil motor for an actuator assembly in a disk
drive system. An estimation is made of a calibration coil
resistance during a calibration operation. A determination is made
of a distance moved during a seek operation. The determined
distance and the calibration coil resistance are used to estimate a
current coil resistance following the seek operation.
Inventors: |
Ho; Peter Kui (Morgan Hill,
CA), Yu; Mantle Man-Hon (San Jose, CA) |
Assignee: |
Hitachi Global Storage Technologies
Netherlands B.V. (Amsterdam, NL)
|
Family
ID: |
28040990 |
Appl.
No.: |
10/107,832 |
Filed: |
March 25, 2002 |
Current U.S.
Class: |
360/78.05;
G9B/5.187 |
Current CPC
Class: |
G11B
5/5521 (20130101) |
Current International
Class: |
G11B
5/55 (20060101); G11B 005/596 () |
Field of
Search: |
;360/71,78.05,75,78.06,78.09,265.8,59,74.7,77.03,78.12,78.13,265.9,264.7,266.4,294.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Advanced Servo-Mechanical Design Facilitates Improved Performance
and Reliability", published by IBM and available on the internet
at: http://www.ibm.com/harddrive, 1999, pp. 1-4. .
S. J. Hwang, "Noise and Vibration Control Technology in Hard Disk
Drives", DataTech, date unknown, pp. 99-106, downloaded from the
Internet on Jan. 29, 2002. .
Y. Li, et al., "Track-Following Controller Design of MEMS Based
Dual-Stage Servos in Magnetic Hard Disk Drives", Computer Mechanics
Lab. Dept. of Mechanical Engineering, University of Berkeley,
California, date unknown. .
Lintech, "Chapter 10. Hard Disk Drives", online, date unknown, pp.
1-20. (Retrieved on Mar. 25, 2001). Retrieved from the Internet at
URL: <http://www.lintech.org/comp-per/index.html>..
|
Primary Examiner: Hudspeth; David
Assistant Examiner: Tzeng; Fred F.
Attorney, Agent or Firm: Victor; David W. Konrad, Raynes,
& Victor LLP
Claims
What is claimed is:
1. A method for estimating coil resistance of a voice coil motor
for an actuator assembly in a disk drive system, comprising:
estimating a calibration coil resistance during a calibration
operation; determining a distance moved during a seek operation;
and using the determined distance and the calibration coil
resistance to estimate a current coil resistance following the seek
operation.
2. The method of claim 1, wherein the distance moved during the
seek operation is moved far a fixed period of time during full
acceleration of the seek operation.
3. The method of claim 1, further comprising: measuring a distance
moved during the calibration operation, wherein the measured
calibration coil resistance and the measured distance moved during
the calibration operation are used to estimate the calibration coil
resistance.
4. The method of claim 3, wherein the distance moved during the
calibration operation is moved for a fixed period of time during
full acceleration of a seek operation.
5. The method of claim 3, further comprising: using the distance
moved during the calibration operation along with the determined
distance moved during the seek operation and the calibration coil
resistance to estimate the current coil resistance.
6. The method of claim 3, further comprising: providing an equation
that correlates a change in distances moved to a change in coil
resistances, wherein the calibration coil resistance is calculated
by: (i) using the equation to determine the change in coil
resistance in a difference of the distance moved during the seek
operation and the distance moved during the calibration operation,
wherein the change in coil resistances comprises the difference of
the coil resistance following the seek operation and the
calibration coil resistance; and (ii) adding the calibration coil
resistance to the determined change in coil resistances to estimate
the coil resistance following the seek operation.
7. The method of claim 6, wherein the equation comprises a solution
of an acceleration function for the voice coil motor that includes
as variables the determined distance and duration and the generated
current for the seek operation to determine the resistance.
8. The method of claim 7, wherein the equation comprises a solution
of a function of a distance moved that is derived from the
acceleration function, wherein the function of the distance moved
comprises:
9. The method of claim 8, wherein the equation comprises a
polynomial solution of the function of the distance moved.
10. The method of claim 1, further comprising: estimating a coil
temperature from the estimated coil resistance following the seek
operation.
11. The method of claim 10, further comprising: using the estimated
coil temperature to modify control output to the voice coil motor
for subsequent seek operations.
12. The method of claim 11, further comprising; determining whether
the estimated coil temperature exceeds a threshold temperature,
wherein modifying the control output comprises reducing power
consumption if the estimated coil temperature exceeds the threshold
temperature.
13. The method of claim 11, wherein the control output to the voice
coil motor is modified in a manner that reduces a likelihood of
track misregistration errors resulting from vibrations of the voice
coil motor.
14. The method of claim 11, further comprising: determining whether
the estimated temperature exceeds a threshold, wherein modifying
the control output to the voice coil motor for subsequent seek
operations comprises lowering a voltage of the determined
subsequent current if the temperature exceeds the threshold.
15. The method of claim 14, wherein the subsequent current is not
adjusted if the temperature does not exceed the threshold.
16. The method of claim 11, further comprising: determining whether
the estimated temperature exceeds a threshold, wherein modifying
the control output to the voice coil motor for subsequent seek
operations comprises delaying application of the subsequent current
to the voice coil motor.
17. The method of claim 11, wherein modifying the control output to
the voice coil motor for subsequent seek operations comprises
adjusting the current to account for a position error signal
independent of the adjustment based on the determined
temperature.
18. The method of claim 1, wherein the seek operation is performed
during normal disk drive operations.
19. A method for estimating coil resistance of a voice coil motor
for an actuator assembly in a disk drive system, comprising:
estimating a calibration coil resistance during a calibration
operation; estimating a coil temperature from the estimated coil
resistance following the seek operation; determining a distance
moved during a seek operation; using the determined distance and
the calibration coil resistance to estimate a current coil
resistance following the seek operation; estimating a resonance
frequency of the voice coil motor from the estimated temperature;
and using the estimated coil temperature to modify control output
to the voice coil motor for subsequent seek operations removing the
determined resonance frequency from a current generated for at
least one subsequent seek operation.
20. The method of claim 19, further comprising: providing a
correlation of temperatures and resonance frequencies for the voice
coil motor, wherein the estimated resonance frequency is determined
from the correlation and the estimated temperature.
21. The method of claim 19, wherein removing the determined
resonance frequency from the generated current further comprises:
determining coefficients to filter the determined resonance
frequency; determining a subsequent current to supply to the voice
coil motor to perform the subsequent seek operation; and applying
the determined coefficients to the determined subsequent current to
filter the determined resonance frequency from the subsequent
current to produce a filtered subsequent current to supply to the
voice coil motor for the subsequent seek operation.
22. An actuator assembly in a disk drive system, comprising: a
voice coil motor; means for estimating a calibration coil
resistance of the voice coil motor during a calibration operation;
means for determining a distance moved during a seek operation; and
means for using the determined distance and the calibration coil
resistance to estimate a current coil resistance of the voice coil
motor following the seek operation.
23. The system of claim 22, further comprising: means for measuring
a distance moved during the calibration operation, wherein the
measured calibration coil resistance and the measured distance
moved during the calibration operation are used to estimate the
calibration coil resistance.
24. The system of claim 23, further comprising: means for using the
distance moved during the calibration operation along with the
determined distance moved during the seek operation and the
calibration coil resistance to estimate the current coil
resistance.
25. The system of claim 23, further comprising: means for providing
an equation that correlates a change in distances moved to a change
in coil resistances; means for using the equation to determine the
change in coil resistance in a difference of the distance moved
during the seek operation and the distance moved during the
calibration operation, wherein the change in coil resistances
comprises the difference of the coil resistance following the seek
operation and the calibration coil resistance; and means for adding
the calibration coil resistance to the determined change in coil
resistances to estimate the coil resistance following the seek
operation.
26. The system of claim 22, further comprising: means for
estimating a coil temperature from the estimated coil resistance
following the seek operation.
27. The system of claim 26, further comprising: means for using the
estimated coil temperature to modify control output to the voice
coil motor for subsequent seek operations.
28. An actuator assembly in a disk drive system, comprising: a
voice coil motor; means for estimating a calibration coil
resistance of the voice coil motor during a calibration operation;
means for estimating a coil temperature from the estimated coil
resistance following the seek operation; means for determining a
distance moved during a seek operation; and means for using the
determined distance and the calibration coil resistance to estimate
a current coil resistance of the voice coil motor following the
seek operation means for estimating a resonance frequency of the
voice coil motor from the estimated temperature; and means for
using the estimated coil temperature to modify output to the voice
coil motor for subsequent seek operations removing the determined
resonance frequency from a current generated for at least one
subsequent seek operation.
29. The system of claim 28, further comprising: means for providing
a correlation of temperatures and resonance frequencies for the
voice coil motor, wherein the estimated resonance frequency is
determined from the correlation and the estimated temperature.
30. An article of manufacture including code for estimated coil
resistance of a voice coil motor for an actuator assembly in a disk
drive system, wherein the code causes operations to be performed,
the operations comprising: estimating a calibration coil resistance
during a calibration operation; determining a distance moved during
a seek operation; and using the determined distance and the
calibration coil resistance to estimate a current coil resistance
following the seek operation.
31. The article of manufacture of claim 30, wherein the distance
moved during the seek operation is moved for a fixed period of time
during full acceleration the seek operation.
32. The article of manufacture of claim 30, further comprising:
measuring a distance moved during the calibration operation,
wherein the measured calibration coil resistance and the measured
distance moved during the calibration operation are used to
estimate the calibration coil resistance.
33. The article of manufacture of claim 32, wherein the distance
moved during the calibration operation is moved for a fixed period
of time during full acceleration of a seek operation.
34. The article of manufacture of claim 32, further comprising:
using the distance moved during the calibration operation along
with the determined distance moved during the seek operation and
the calibration coil resistance to estimate the current coil
resistance.
35. The article of manufacture of claim 32, further comprising:
providing an equation that correlates a change in distances moved
to a change in coil resistances, wherein the calibration coil
resistance is calculated by: (i) using the equation to determine
the change in coil resistance in a difference of the distance moved
during the seek operation and the distance moved during the
calibration operation, wherein the change in coil resistances
comprises the difference of the coil resistance following the seek
operation and the calibration coil resistance; and (ii) adding the
calibration coil resistance to the determined change in coil
resistances to estimate the coil resistance following the seek
operation.
36. The article of manufacture of claim 35, wherein the equation
comprises a solution of an acceleration function for the voice coil
motor that includes a variables the determined distance and
duration and the generated current for the seek operation to
determine the resistance.
37. The article of manufacture of claim 36, wherein the equation
comprises a solution of a function of a distance moved that is
derived from the acceleration function, wherein the function of the
distance moved comprises:
38. The article of manufacture of claim 37, wherein the equation
comprises a polynomial solution of the function of the distance
moved.
39. The article of manufacture of claim 30, further comprising:
estimating a coil temperature from the estimated coil resistance
following the seek operation.
40. The article of manufacture of claim 39, further comprising:
using the estimated coil temperature to modify control output to
the voice coil motor for subsequent seek operations.
41. The article of manufacture of claim 40, further comprising;
determining whether the estimated coil temperature exceeds a
threshold temperature, wherein modifying the control output
comprises reducing power consumption if the estimated coil
temperature exceeds the threshold temperature.
42. The article of manufacture of claim 40, wherein the control
output to the voice coil motor is modified in a manner that reduces
a likelihood of track misregistration errors resulting from
vibrations of the voice coil motor.
43. The article of manufacture of claim 40, further comprising:
determining whether the estimated temperature exceeds a threshold,
wherein modifying the control output to the voice coil motor for
subsequent seek operations comprises lowering a voltage of the
determined subsequent current if the temperature exceeds the
threshold.
44. The article of manufacture of claim 43, wherein the subsequent
current is not adjusted if the temperature does not exceed the
threshold.
45. The article of manufacture of claim 40, further comprising:
determining whether the estimated temperature exceeds a threshold,
wherein modifying the control output to the voice coil motor for
subsequent seek operations comprises delaying application of the
subsequent current to the voice coil motor.
46. The article of manufacture of claim 40, wherein modifying the
control output to the voice coil motor for subsequent seek
operations comprises adjusting the current to account for a
position error signal independent of the adjustment based on the
determined temperature.
47. The article of manufacture of claim 30, wherein the seek
operation is performed during normal disk drive operations.
48. An article of manufacture including code for estimating coil
resistance of a voice coil motor for an actuator assembly in a disk
drive system, wherein the code causes operations to be performed,
the operations comprising: estimating a calibration coil resistance
during a calibration operation; estimating a coil temperature from
the estimated coil resistance following the seek operation;
determining a distance moved during a seek operation; using the
determined distance and the calibration coil resistance to estimate
a current coil resistance following the seek operation; estimating
a resonance frequency of the voice coil motor from the estimated
temperature; and using the estimated coil temperature to modify
control output to the voice coil motor for subsequent seek
operations removing the determined resonance frequency from a
current generated for at least one subsequent seek operation.
49. The article of manufacture of claim 48, further comprising:
providing a correlation of temperatures and resonance frequencies
for the voice coil motor, wherein the estimated resonance frequency
is determined from the correlation and the estimated
temperature.
50. The article of manufacture of claim 48, wherein removing the
determined resonance frequency from the generated current further
comprises: determining coefficients to filter the determined
resonance frequency; determining a subsequent current to supply to
the voice coil motor to perform the subsequent seek operation; and
applying the determined coefficients to the determined subsequent
current to filter the determined resonance frequency from the
subsequent current to produce a filtered subsequent current to
supply to the voice coil motor for the subsequent seek operation.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method, system, and program for
estimating coil resistance of a Voice Coil Motor (VCM) in a disk
drive system.
2. Description of the Related Art
Computer hard disk drives include one or more disks of magnetic
storage medium and a disk drive head assembly to read and write
data on the magnetic storage medium. Magnoresistive (MR) heads
typically include a write element comprised of a thin film
inductive head and a read element comprised of a sensor. MR heads
for the disk surfaces of the disk drive are affixed to an actuator
or arm that glides across the disk surface to position the head at
different track locations. Current is passed to a voice coil motor
(VCM) to position the actuator with respect to the disk surface.
The amount of torque applied to the actuator is governed by the
amount of current in the VCM. The VCM comprises the coil that
receives the current and two magnets. During operations, the disk
drive components, such as the VCM, can produce vibrations induced
as a result of the resonance of the components. Such vibrations may
result in undesirable head variations and tracking errors.
One factor leading to an increase demand in attenuating vibrations
and noise produced by the VCM is the increased demand for higher
storage capacity and faster Input/Output (I/O) access in disk
drives. High disk operation speeds require higher voltages to
generate more current to the VCM so that sufficient torque is
created to actuate movement of the actuator (head-arm) assembly at
the higher speeds. Higher voltages subjects the VCM to greater
acoustic and mechanical energy, which may result in increased noise
and vibrational problems.
In current disk drive systems, to correct for tracking errors
resulting from noise and vibrations from components such as the
VCM, the disk drive controller will read servo information
indicating the actual current position and compare that value read
to the desired position. The drive controller will then calculate a
current to apply to the VCM to correct any variation in the
measured position versus desired position. Thus, the current
supplied to the VCM to apply torque to the actuator arm is a
function both of the amount of current in the voice coil supplied
by an amplifier controlled by the drive controller and by position
feedback adjustments based on position information read from the
data heads.
Other techniques to reduce VCM vibrational noise includes the use
of lighter and stiffer suspension elements in the actuator that
have much higher natural frequencies. Also smaller and lighter
slider designs provide less contact areas for the transmission of
vibrations and noise from the VCM. However, there are design
constraints on further reductions in size of the actuator to reduce
vibrations and noise. Another solution to alleviate noise is to use
suspension dampers to dissipate energy transmitted through the
actuator and reduce the amount of vibrations and noise produced by
the VCM.
Notwithstanding the current efforts to reduce the vibrations and
noise produced by the VCM, there is a continued need in the art to
attenuate the effect of vibrations and noise emanating from the VCM
on disk drive performance.
SUMMARY OF THE PREFERRED EMBODIMENTS
Provided are a method, system, and program for estimating coil
resistance of a voice coil motor for an actuator assembly in a disk
drive system. An estimation is made of a calibration coil
resistance during a calibration operation. A determination is made
of a distance moved during a seek operation. The determined
distance and the calibration coil resistance are used to estimate a
current coil resistance following the seek operation.
In further implementations, a distance moved during the calibration
operation is measured. The measured initial coil resistance and the
measured distance moved during the calibration operation are used
to estimate the calibration coil resistance.
An equation is provided that correlates a change in distances moved
to a change in coil resistances. The calibration coil resistance is
calculated by using the equation to determine the change in coil
resistance from the distance moved during the calibration
operation. The change in coil resistance is the difference of the
coil resistance following the seek operation and the calibration
coil resistance. The calibration coil resistance is added to the
determined change in coil resistances to estimate the coil
resistance following the seek operation.
Still further, a coil temperature may be estimated from the
estimated coil resistance following the seek operation.
Yet further, the estimated coil temperature may be used to modify
control output to the voice coil motor for subsequent seek
operations.
The described implementations provide techniques for estimating the
coil resistance and temperature with an improved degree of accuracy
using both the distance and duration of a previous seek operation.
The estimated temperature may then be used to modify control output
to improve the performance of disk drive operations, such as by
generate a voice coil motor current in a manner that reduces a
likelihood of track misregistration errors resulting from
vibrations of the voice coil motor.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings in which like reference numbers
represent corresponding parts throughout:
FIG. 1 illustrates a disk drive architecture in which aspects of
the invention are implemented;
FIG. 2 illustrates curves providing a correlation of a change in
distances moved by the actuator head and a change in coil
resistances in accordance with implementations of the invention;
and
FIGS. 3 and 4 illustrate logic to estimate the coil resistance and
temperature of the voice coil motor and adjust the current in
accordance with implementations of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description, reference is made to the accompanying
drawings which form a part hereof and which illustrate several
embodiments of the present invention. It is understood that other
embodiments may be utilized and structural and operational changes
may be made without departing from the scope of the present
invention.
FIG. 1 illustrates a disk drive system 2, including one or more
rotating disks 4 (only one is shown), an actuator assembly 6 to
move a head assembly 8 across the disk 4 surface. The disk drive
system 2 further includes a current driver 10 that converts the
digital signal of a calculation from servo electronics 12 or
processor 18 to actual current that is applied to a voice coil
motor (VCM) 14. The VCM 14 comprises a coil that sits between two
magnets. The current driver 10 applies current to the VCM 14 to
cause the coil to react and move through a magnetic field to move
the actuator 6.
In certain implementations, the head 8 is a magnetoresistive (MR)
head device. However, in alternative implementations, the head 8
may be constructed of other materials known in the art. The servo
electronics 12 provides a closed loop feedback system to insure
that the head follows the tracks accurately and to control smooth
transitions when the head "seeks" from one track location to
another track. The servo electronics 12 calculates the position
error signal (PES) from the actual position data and from
pre-recorded servo information either on a dedicated servo disk or
on servo sectors interspersed among the data sectors on the disk.
The servo electronics 12 uses the servo information to determine
PES, which is the signal proportional to the difference between the
ideal center line tracking and the actual positions of the head
assembly 8. The servo electronics 12 may then calculate a
corrective position signal based on the PES. The actuator 6 pivots
around a shaft 16 in response to the torque produced by the VCM
14.
A processor 18 manages read/write operations and controls other
disk operations. The processor 18 may perform certain of the
operations to calculate PES, NRRO, and determine a corrective
signal. Alternatively, the servo electronics 12 may calculate the
PES and NRRO in manners known in the art. The processor 18 utilizes
a volatile memory 20, such as a random access memory (RAM) or
registers as a working memory in which instructions and data are
temporarily loaded for program execution. A non-volatile storage
22, such as a read-only memory (ROM), programmable ROM (PROM),
electronically programmable ROM (EPROM), flash memory, etc., stores
program instructions and constants, referred to as code 26, loaded
and executed by the processor 18 to perform the disk drive
operations. Alternatively, the code 26 described herein as
performed by processor 18 along with the volatile memory 20 and
non-volatile storage 22 may be implemented as hardware, such as an
Application Specific Integrated Circuit (ASIC).
In the described implementations, the processor 18 estimates the
temperature of the VCM 14 for use in determining an adjustment
signal to transmit to the current driver 10 to control the current
supplied to the VCM 14 to move the actuator arm 6. With the
described implementations, temperature is measured during intended
customer use. In order to estimate coil resistance during seek
operations, in certain implementations the non-volatile storage 22
may maintain a coil resistance equation 24 that provides a
correlation of a distance the actuator head moves to coil
resistance of the VCM 14.
The distance traveled by a head can relate to the coil resistance
of the VCM 14 by considering the equation for acceleration of the
head assembly 8, which can be calculated as shown in equation (1)
below:
acc(t)=(kt*L)/J*(Vcoil-Velocity*kt)/Rcoil (1)
In the above equation (1) to calculate acceleration (acc) as a
function of time, the following variables and constants are
used:
kt=the torque constant of the VCM 14, which is the amount of torque
generated per unit of current.
L=the length constant, which is the length of the actuator assembly
6 between the head assembly 8 and the pivot point 16.
J=is a constant of the inertia of the VCM 14.
Vcoil=the voltage applied to the VCM 14 during the seek operation,
may vary between seek operations.
Velocity=the angular velocity variable of the VCM 14 during the
seek operation.
Rcoil=the coil resistance, which is the variable to calculate.
The distance (x) the head assembly 8 travels between the time of
the seek from t.sub.0 to t.sub.1 is modeled by the following
equation (2) below: ##EQU1##
The Velocity is the speed traveled between the seek distance during
the seek duration. The solution to the above differential equation
for a distance (x) traveled may be expressed as equation (3)
below:
where .tau.=Rcoil*J/kt.sup.2
Numerical analysis techniques known in the art can be used to
provide a polynomial approximation of equation (3) that correlates
resistance as a function of a change in distance moved. In certain
implementations, the solution of equation (3) provides an equation
that correlates a change in distance moved (X.sub.change) and a
change in coil resistance (R.sub.change), calculated as follows
according to equations (4) and (5):
x.sub.change =x.sub.n -x.sub.0 (4)
where Rcoil.sub.n is the coil resistance measured at a time n after
the actuator assembly 6 is moved a distance x.sub.n, and
Rcoil.sub.0 is an initial coil resistance measured after the
actuator assembly 6 moves an initial distance (x.sub.0), such as
during calibration. FIG. 2 illustrates curves generated as the
first order 50, second order 52, and third order 53 polynomial
solutions to equation (3) as a function of the R.sub.change and
x.sub.change. Below is an example of three different equations (6),
(7), and (8) modeling the curves 50, 52, and 54, respectively,
which provide numerical polynomial approximations of equation (3).
##EQU2##
The above equation polynominal solutions of equations (6), (7), and
(8) are calculated based on a particular set of coil parameters
(kt, L, J, Vcoil) using numerical analysis algorithms. Alternative
polynominal equations may be generated for different coil
parameters.
The coil resistance equation 24 in the non-volatile storage 22 may
be any one of the equations (6), (7), and (8), or any other
equation providing a solution to equation (3) or a correlation of
coil resistance and seek distance moved by the actuator head 8. The
particular coil resistance equation 24 selected would depend upon
the computational capabilities of the processor 18. The higher
order polynomial solution, e.g., equation (8), may be used with
more powerful processes, whereas the lower order polynomial, e.g.,
equation (6), may be used for less powerful processors.
FIG. 3 illustrates logic implemented in code 26 in the non-volatile
storage 22 loaded and executed by the processor 18 to determine a
calibration coil resistance for a seek distance moved during
calibration that is used to determine the coil resistance during
subsequent seek operations. Control begins at block 100 during the
disk initialization routine. During initialization, the processor
18 generates (at block 102) a signal for a fixed voltage to the VCM
14 while the actuator assembly 6 is positioned against a crash stop
and determines the calibration coil resistance (Rcoil.sub.cal) as
the applied voltage divided by the measured resultant current
(voltage/current) to be used in subsequent operations. In
alternative implementations, the coil resistance can be measured by
twice applying voltage to the VCM 14 while the actuator assembly 6
is stationary at the crash stop. In such cases, the processor 18
would measure the corresponding coil current during each movement,
and then measure coil resistance according to equation (9)
below:
Voltage 1 is applied with the actuator assembly 6 positioned
against the crash stop and the resultant coil current 1 is
measured. Next, voltage 2 is applied and the resultant coil current
2 is measured. From such gathered data, the initial coil resistance
(Rcoil.sub.1) can be measured according to equation (9) above.
After measuring this calibration coil resistance (Rcoil.sub.cal),
the processor 18 measures a calibration distance (x.sub.cal) by
applying a fixed voltage to the VCM 14 to measure the distance
(x.sub.cal) traveled at full acceleration for a fixed period of
time. The distance measured may be in units of tracks. The
processor 18 then buffers (at block 106) in volatile memory 20 the
distance moved during calibration (x.sub.cal) and the estimated
calibration coil resistance (Rcoil.sub.cal) for use in subsequent
seek operations.
FIG. 4 illustrates logic implemented in the code 26 in the
non-volatile memory 22, which is loaded and executed by the
processor 18 to measure the coil resistance during seek operations
during use of the disk drive 2 and utilize such measured coil
resistance. Upon performing a seek operation (at block 150) during
normal disk 2 operations, the distance the actuator head 8 moves
during the seek (x.sub.n) for a fixed period of time during full
acceleration is measured (at block 152). The change in distance
(x.sub.change) is then calculated (at block 154) as the distance
moved during the seek (x.sub.n) minus the buffered seek distance
moved during calibration (X.sub.cal). The processor 18 then uses
the coil resistance equation 24 to calculate (at block 156) the
change in coil resistance (R.sub.change) as a function of the
measured change in distance (x.sub.change). The coil resistance for
the current seek (Rcoil.sub.n) is then calculated by adding (at
block 158) the coil resistance at calibration (Rcoil.sub.cal) to
the determined change in coil resistance (R.sub.change)
After estimating the current coil resistance following the seek
operation (Rcoil.sub.n), the code 26 may provide further algorithms
for utilizing the current coil resistance to improve disk drive 2
performance. For instance, at block 160, the processor 18 uses the
calculated coil resistance (Rcoil.sub.n) to estimate the
temperature of the VCM 14. The code 26 may maintain an empirically
determined correlation of coil resistance to temperature for the
particular VCM 14, to perform the operation at block 160 to
calculate the temperature from the determined coil resistance. The
processor 18 may then estimate (at block 162) the resonance
frequency from the determined temperature from an empirically
determined correlation of resonance frequencies and temperatures
for the particular VCM 14 maintained in the code 26 non-volatile
storage 22. The processor 18 would then determine (at block 164)
the current needed to control the voice coil motor 14 to perform
the seek operation, i.e, move the head assembly 8 from the current
to the desired position. In determining the current to apply, the
processor 18 may read position information from the disk to
determine a position error signal (PES) to minimize track
misregistration and/or Non-Repeatable Run Out (NRRO) errors in a
manner known in the art. The processor 18 then filters (at block
166) the determined current to remove the determined resonance
frequency for the determined temperature. The result is a current
attenuated for the frequency correlated with the estimated
temperature.
In further implementations, the measured coil resistance at block
158 may be used to estimate temperature to monitor the temperature
of the VCM 14 in order to prevent overheating. If the VCM 14 is
reaching a temperature threshold, then the processor 18 may modify
the velocity profile of the actuator assembly. Those skilled in the
art will appreciate that there are alternative uses of the
temperature estimated during disk operations to improve disk drive
performance 2.
In an alternative implementation, the coil resistance equation 24
may provide a solution of equation (3) as a function of the
distance (x) and duration of the seek (t) at block 104, using the
known constants, such as Kt, L, J maintained in the non-volatile
storage 22, as well as the variable of the applied voltage (Vcoil)
supplied by the processor 18.
In still further implementations, the calibration coil resistance
(Rcoil.sub.cal) may be used to determine a coil resistance error
offset that is the difference of the calibration coil resistance
(Rcoil.sub.cal) and the initial measured coil resistance
(Rcoil.sub.i) when the actuator assembly 16 is positioned against
the crash stop. This error offset may then be applied to any
subsequently determined coil resistance (Rcoil.sub.n) calculated
during normal seek operations.
In certain implementations, at block 106, the processor 18 would
use the equation (3) to estimate the resistance of the VCM 14
during disk operations to estimate temperature. In alternative
implementations, the processor 18 may use an empirically determined
correlation between velocity and a change of resistance to estimate
the change of resistance based on the velocity of the seek
operation. This relationship of velocities and resistance changes
may be maintained in the non-volatile storage 22 as a table. The
estimated change of resistance would be applied to the previously
determined resistance, buffered in the volatile memory 20, to
determine the current resistance as a function of the velocity of
the performed seek operation.
With the described implementations, coil resistance and temperature
are estimated during normal disk operations and used to adjust disk
operations to optimize performance. For instance, the estimated
temperature may be used in a feedback system to eliminate the
resonance frequency of the VCM 14 and thereby substantially reduce
noise and vibrations resulting from the VCM 14. To filter out the
resonance frequency, the processor may determine filter function
adjustment coefficients that can eliminate the resonance frequency
from an input signal. The processor 18, or other circuitry, would
then use a position readback signal to derive the broadband
actuating signal to move the head 8 to the target location, taking
into account any position error signal (PES) or NRRO adjustments
known in the art that are used to reduce track misregistration. The
processor 18 may then apply the coefficients to the derived current
needed to move the actuator assembly 6 to the target position to
remove the resonance frequency. In certain implementations, a
separate filter, such as a notch filter, may be used to remove the
resonance frequency. Further details of using a notch filter to
filter a signal to remove the resonance frequency is described in
the commonly assigned U.S. Pat. No. 6,188,191, which patent is
incorporated herein by reference in its entirety.
Further, the described implementations provide a technique for
estimating the current temperature of the VCM 14 with a high degree
of accuracy without having to provide for additional sensors or
hardware structures. Instead, the processor 18, or other control
circuitry, can estimate the temperature using information generated
during seek operations during normal customer use of the drive.
ADDITIONAL IMPLEMENTATION DETAILS
The described logic for estimating coil resistance and using such
coil resistance in disk drive operations may be implemented as a
method, apparatus or article of manufacture using standard
programming and/or engineering techniques to produce software,
firmware, hardware, or any combination thereof. The term "article
of manufacture" as used herein refers to code or logic implemented
in hardware logic (e.g., an integrated circuit chip, Programmable
Gate Array (PGA), Application Specific Integrated Circuit (ASIC),
etc.) or a computer readable medium, such as magnetic storage
medium (e.g., hard disk drives, floppy disks,, tape, etc.), optical
storage (CD-ROMs, optical disks, etc.), volatile and non-volatile
memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs,
firmware, programmable logic, etc.) Code in the computer readable
medium is accessed and executed by a processor. The code in which
preferred embodiments are implemented may further be accessible
through a transmission media or from a file server over a network.
In such cases, the article of manufacture in which the code is
implemented may comprise a transmission media, such as a network
transmission line, wireless transmission media, signals propagating
through space, radio waves, infrared signals, etc. Of course, those
skilled in the art will recognize that many modifications may be
made to this configuration without departing from the scope of the
present invention, and that the article of manufacture may comprise
any information bearing medium known in the art.
In the described implementations, the temperature was used to
estimate a resonance frequency of the VCM 14 for use in determining
dampening coefficients to apply to the current to remove the
resonance frequency. In additional implementations, the determined
temperature may be used to determine other ways to modify the VCM
current to reduce the likelihood of track misregistration, errors,
and damage to the disk drive. For instance, the estimated
temperature may be used to determine a corresponding delay to apply
before transmitting the current to the VCM 14, i.e., a cooling-off
period, if the VCM 14 temperature exceeds an upper threshold.
Still further, the current signal may be attenuated in ways other
than removing the resonance frequency to reduce the likelihood of
tracking errors. For instance, applying sufficient current to the
VCM 14 at high temperatures can degrade and damage the VCM 14, such
as by degrading the laminations on the coil. In certain
implementations, upon detecting upper threshold temperatures for
the VCM 14, the current supplied to the VCM 14 can be reduced to
avoid degradation to the VCM 14 structure.
The described implementations included a specific equation for use
in estimating the coil resistance. In alternative implementations,
different equations related to acceleration may be used to estimate
resistance. Alternatively, equations not related to acceleration
may also be used to estimate resistance.
Certain implementations were described with respect to MR heads.
However, the head assembly 8 may be implemented with read and/or
write heads other than MR heads, e.g., ferrite, MIG, thin film,
GMR, one-sided, two-sided, etc., to determine non-mechanical noise
arising from structural defects.
The described implementations may be implemented in disk drives
that include multiple platters and multiple heads to read from one
or both surfaces of each platter.
The foregoing description of the preferred embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention be limited not by this
detailed description, but rather by the claims appended hereto. The
above specification, examples and data provide a complete
description of the manufacture and use of the composition of the
invention. Since many embodiments of the invention can be made
without departing from the spirit and scope of the invention, the
invention resides in the claims hereinafter appended.
* * * * *
References